The present invention generally relates to the preparation of molecular or ionic supramolecular assemblies, and more particularly to the formation of nanometer scale structures, having a substantially enclosed volume.
Encapsulation of one chemical species by another, sometimes termed xe2x80x9chost-guest chemistryxe2x80x9d, is a phenomenon that has a wide range of applicability. For example, encapsulation technology is presently used to produce pressure-sensitive inks for carbon copies and is of interest for use in drug delivery. Encapsulation could play an important role in modifying the physical properties of drug substances to enhance their compounding properties for oral and topical administration. Encapsulation could also be important for development of nano-devices, where it could provide a way of insulating molecular wires from each other much as the myelin sheath functions on neurons. In view of the importance and variety of context in which encapsulation plays a critical role, it would be desirable to control the volume within which a species is encapsulated by another. It would be particularly desirable to have a way in which to control the volume enclosed by an encapsulating species without changing fundamentally the composition, and therefore the chemical reactivity, of that species.
The present invention provides a way of controlling the volume enclosed by encapsulating species and controlling the topology of that enclosed volume. An encapsulating or xe2x80x9cclathratingxe2x80x9d species that exists either as a spherical cluster or as a tubule is prepared by varying the proportions of the constituents of the encapsulating species.
More specifically, the inventors have found that variation in the proportion of a co-ligand added to a mixture of a calix[4]arene bearing a potential ligating group in the para-position and a n+ metal ion (where n=2-3) changes the topology of the solid-state structure into which the species assembles. Still more specifically, the applicants have found pyridine-N-oxide to be especially useful as a co-ligand when used in conjunction with p-sulfonatocalix[4]arene complexed to lanthanide(III) species.
Accordingly, in carrying out the present invention, there is provided a composition comprising a calixarene, a co-ligand, and a 2+ or 3+ metal ion in a ratio of about 1:1:1 to about 2:8:1. Preferably the calixarene has the structure 
wherein Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3, and Rxe2x80x3xe2x80x3 are functional groups capable of binding to a metal ion. More, specifically, Rxe2x80x2, Rxe2x80x3, and Rxe2x80x2xe2x80x3, and Rxe2x80x3xe2x80x3 can be the same or different and are independently selected from the group consisting of amino, sulfonate, carboxylate, hydroxamate, phosphonate, and pyridyl groups.
In a further aspect of the invention, the metal ion of the above composition is an element with atomic number Z, which is 12 and/or within the ranges of 20-31, 38-50, and 56-82. In a specific embodiment of the invention, the metal ion is selected from the group consisting of calcium, cadmium, copper, yttrium, and lanthanum. The co-ligand is selected from the group consisting of heterocyclic N-oxides, phenols, anilines, and nitrobenzenes. More specifically, the co-ligand is selected from the group consisting of pyridine N-oxide, quinoline-N-oxide, phenol, aniline, and nitrobenzene.